The present invention relates to a method for the production of a liner comprising in at least a top layer and a base layer, wherein a forming section with at least two forming units is used to create a fiber web, said fiber web being conveyed through a press section and further to a drying section, said press section comprising a number of roll nips and at least one impermeable transfer belt with at least one smooth surface. The invention also relates to a paper machine for realization of the method.
A liner, a form of multilayer board, comprises frequently a top layer, which is intended for printing. This top layer must display a high smoothness in order to achieve good printability. For production of the surface layer, bleached pulp is preferably used, more particularly, pulp which is bleached to high brightness and which contains short fibers.
Different methods and machines for the production of multilayer board are described in a number of different documents in the patent literature, e.g., EP 1 076 606, U.S. Pat. No. 5,681,431, U.S. Pat. No. 5,178,732, EP 0 511 186, WO 92/06242, U.S. Pat. No. 4,961,824, EP 0 511 185, U.S. Pat. No. 5,074,964, EP 0 233 058 and SE 506 611. However, none of these documents teach how to produce multilayer board, i.e. a liner, wherein a layer intended for printing can acquire a very good printability in a high speed process.
The above and other needs are met by the present invention which, in one embodiment, provides a method for the production of a liner comprising at least a top layer and a base layer. A forming section is provided, having at least two forming units to create a fiber web. A press section is provided, comprising a number of rolls and a transfer belt with at least one smooth surface, wherein at least some of said rolls form roll nips comprising a last roll nip for conveying said fiber web through the press section and further to a drying section. By moving said transfer belt through the last nip in the press section, the fiber web is conveyed through the last nip of the press section in such a manner that the layer intended for printing of the web is pressed against said smooth surface of the transfer belt. In this manner, the layer intended for printing acquires a very good printability, wherein the fiber web is simultaneously transferred through the press section at a relatively higher speed.
In accordance with further aspects of the method:
the fiber web is exposed to a liner load of between 600-2000 KN/m in said last nip,
the fiber web W is conveyed through at least three nips in the press section and
the fiber web W in the next-to-last nip is exposed to a linear load of between 30-150 KN/m,
the fiber web W, before the next-to-last nip, is conveyed through a leading nip which consists of a shoe press and under a linear load of between 200-1000 kN/m,
the fiber web W, before the next-to-last nip, is conveyed through a leading nip which consists of a press and under a linear load of between 50-200 kN/m,
the base layer is formed of unbleached pulp which is substantially long-fibered and preferably contains fir and/or pine fibers and the top layer is formed of a pulp, which at least partially contains short fibers such as birch or eucalyptus fibers, wherein the pulp for the top layer is also preferably bleached.
the grammage of the completed liner is 60-205 g/m2, preferably 60-150 g/m2.
the fiber web W is conveyed through the press section P at a speed of 750-2000 m/min, preferably exceeding 1000 m/min, more preferably exceeding 1200 m/min,
the layer intended for printing consists of bleached pulp,
the layer intended for printing contains at least 30 weight-% of short fibers,
the layer intended for printing contains at least 50 weight-% of short fibers.
the layer intended for printing is formed on top of the base layer in the forming section, so that layer intended for printing of the fiber web constitutes the upper layer of the web W.
Embodiments of the invention also relate to a paper machine for production of a liner, comprising a forming section and a press section, said forming section comprising at least two forming units in order to permit production of a fiber web with at least two layers of which one layer constitutes a top layer, said press section comprising a plurality of rolls and a transfer belt with at least one smooth surface, wherein at least some of said rolls form roll nips comprising a last nip, wherein said last nip is through-fed by said transfer belt and arranged such that its smooth surface is directed against the layer intended for printing of the fiber web when the fiber web runs through said last nip.
In accordance with further aspects of the paper machine:
the smooth surface of the transfer belt is directed away from an upper press roll in said last nip, said last nip preferably comprising a shoe press unit;
the press section comprises at least three nips, wherein preferably the next-to-last nip consists of a press,
said three nips are achieved with four roll units,
said three nips are achieved with five roll units, wherein preferably the first of said three nips comprises a shoe press,
said transfer belt is impermeable.
Further, the invention relates to a method for production of a liner comprising at least one layer of bleached pulp and one layer of unbleached pulp. A forming section is provided, having at least two forming units to create a fiber web. A press section is provided, comprising a number of rolls and one transfer belt with at least one smooth surface, wherein at least some of said rolls form roll nips comprising a last nip for conveying said fiber web through the press section and further to a drying section, wherein said transfer belt is moved through said last nip of the press section in such a manner that the layer of bleached pulp is pressed against said smooth surface of the transfer belt.
Finally, the invention relates to a method for production of a liner comprising at least one layer of pulp containing at least 30 weight-% of short fibers and one layer of pulp containing essentially long fibers. A forming section is provided, having at least two forming units for creating a fiber web. A press section is provided, comprising a number of rolls and one transfer belt with at least one smooth surface, wherein at least some of said rolls form roll nips comprising a last nip for conveying said fiber web through the press section and further to a drying section, wherein said transfer belt runs through the last nip in the press section and the fiber web is conveyed through the last nip in the press section in such manner that the layer consisting of at least 30 weight-% of short fiber pulp is pressed against said smooth surface of the transfer belt.